HHS Special Exposure Cohort Designation:

Blockson Chemical Company, Joliet, Illinois 

HHS Designation of Additional Members of the 

Special Exposure Cohort 

under the 

Energy Employees Occupational Illness Compensation Program Act of 2000 

Designating a Class of Employees from 

Blockson Chemical Company

Joliet, Illinois 
HHS Special Exposure Cohort Designation: 

Blockson Chemical Company, Joliet, Illinois Page 2

I. Designation 

I, Kathleen Sebelius, Secretary of Health and Human Services, designate the class 

of employees defined in Section II of this report for addition to the Special Exposure 

Cohort (SEC), as authorized under the Energy Employees Occupational Illness 

Compensation Program Act of 2000 (EEOICPA), 42 U.S.C. § 7384q.

___September 3, 2010__ ___[Signature on file]________

Date Kathleen Sebelius

II. Employee Class Definition

All Atomic Weapons Employer employees who worked at the Blockson 

Chemical Company in Joliet, Illinois from March 1, 1951 to June 30, 1960, for 

a number of work days aggregating at least 250 work days, occurring either 

solely under this employment or in combination with work days within the 

parameters established for one or more other classes of employees in the 

Special Exposure Cohort. 

III. Designation Criteria and Recommendations

Pursuant to 42 U.S.C. § 7384q, for the class defined in Section II of this report, the 

Secretary has determined, and the Advisory Board on Radiation and Worker Health 

(Board) has recommended, that

(1) it is not feasible to estimate with sufficient accuracy the radiation dose that the 

class received; and

(2) there is a reasonable likelihood that such radiation dose may have 

endangered the health of members of the class.

The SEC final rule states in 42 C.F.R. § 83.13(c)(1) that it is feasible in two situations 

to estimate the radiation dose that the class received with sufficient accuracy. First, 

the rule states that radiation doses may be estimated with sufficient accuracy if 

NIOSH has established that it has access to sufficient information to estimate the 

maximum radiation dose for every type of cancer for which radiation doses are 

reconstructed that could have been incurred under plausible circumstances by any 

member of the class. Alternatively, radiation doses may be estimated with sufficient 

accuracy if NIOSH has established that it has access to sufficient information to 

estimate the radiation doses of members of the class more precisely than a 

maximum dose estimate.

The Board, pursuant to 42 U.S.C. § 7384q, advised the Secretary to designate the 

class as an addition to the SEC in a letter received by the Secretary on August 9, 

2010.
HHS Special Exposure Cohort Designation: 

Blockson Chemical Company, Joliet, Illinois Page 3

IV. Designation Findings

Feasibility of Estimating Radiation Doses with Sufficient Accuracy

The Secretary established the feasibility determination for the class of employees 

covered by this report based upon the findings summarized below.

• The principal source of internal radiation exposures for members of the proposed 

class at Blockson Chemical Company was exposure to naturally occurring 

radioactive constituents contained in phosphate rock, radon, natural uranium and 

thorium, and their associated progeny.

• NIOSH evaluated the feasibility of completing dose reconstructions for all Atomic 

Weapons Employer personnel who worked on activities related to the production 

of uranium at Blockson Chemical Company, Joliet, Illinois, from January 1, 1951

through December 31, 1962. However, the beginning date of the class definition 

was changed to accurately reflect the time period of the Atomic Energy 

Commission contract with Blockson which began on March 1, 1951. The end 

date also was changed to June 20, 1960, to be consistent with a March 2010 

determination by the Department of Labor (DOL) that the covered period ended 

on that date. 

• NIOSH, in its Evaluation Report, found that no air sampling results are available 

for estimating intakes for Blockson workers. However, uranium urinalysis results 

(the preferred method of estimating internal doses received from exposure to 

uranium) are available for some Blockson workers. NIOSH has records and data 

from 122 urine samples from 25 different employees collected from April, 1954 to 

February, 1958 (nineteen employees have multiple samples). Ten records of the

urinalyses are available, with results for 12 to 13 workers on each record. 

• NIOSH believed that internal dose reconstruction for members of the proposed 

class was feasible, based on the following: (1) the availability of representative 

personnel uranium internal monitoring data for workers in Building 55; (2) the 

application of 95th percentile doses that are bounding for workers; (3) the use of 

claimant-favorable assumptions with regard to other non-uranium radionuclides 

and potential intakes in plant areas outside of Building 55; and 4) the 

development of a probabilistic source-term model to reconstruct radon exposures 

in Building 40.

• The NIOSH Evaluation Report states that no radon monitoring data are available 

for the period of uranium operations at Blockson. In order to estimate radon dose

for claimants, NIOSH developed a probabilistic model to estimate radon 

concentrations in Building 40. 

• The proposed NIOSH model calculates the average radon concentration in

Building 40, and the uncertainty distribution generated by the model is the 

uncertainty distribution of the average concentration. If there is stratification of

radon concentrations in the building, the distribution of actual concentrations in

the building may not be the same as the distribution of average concentrations 

generated by the radon model. Consequently, the 95th percentile of the actual 
HHS Special Exposure Cohort Designation: 

Blockson Chemical Company, Joliet, Illinois Page 4

building concentrations may not be the 95th percentile of the average building 

concentrations. While some worker accounts indicate that workers moved 

around the building during a shift, it does not necessarily follow that any given 

worker’s exposure can be characterized by the distribution of the calculated 

average building concentration, as opposed to the distribution of the actual 

concentrations due to stratification.

• NIOSH has not been able to locate data or a situation it could use to validate the 

model. There are virtually no monitoring data from phosphate plants from the 

50’s or 60’s. NIOSH has not reconstructed doses by modeling radon exposure at 

any other covered facilities. However the general form of the model proposed by 

NIOSH is included in existing methods for performing dose estimates in other 

applications. Specifically, RESRAD, a Nuclear Regulatory Commissionsponsored collection of models for estimating radiation exposures due to 

contaminated environs which is used in environmental remediation, contains a 

radon model of the general form proposed by NIOSH. Consequently, NIOSH’s 

opinion was that the wide acceptance of methods like those in RESRAD obviated 

the need for site-specific validation.

• The lack of any radon monitoring data from the years of the proposed SEC class, 

or from a time period even particularly close to those years, carries weight as an 

argument to support adding the class. It would certainly have strengthened

NIOSH’s proposed approach if NIOSH had been able to identify supporting 

contemporaneous radon measurements from Blockson, or even from other 

similarly-constructed facilities that performed the same or similar

functions. Therefore, it is not feasible to reconstruct radiation doses associated 

with exposure to radon gas and its short-lived progeny with sufficient accuracy 

for the period from March 1, 1951 to June 30, 1960. 

• The principal source of external radiation exposure for members of the proposed 

class was exposure to naturally occurring radioactive constituents contained in 

phosphate rock, yellowcake, natural uranium and thorium, and all their 

associated progeny. 

• No external dosimetry data are known to exist for Blockson workers, and NIOSH 

data capture efforts did not find any direct radiation survey results from the 

Blockson facility. Therefore, source term information was used to estimate 

external doses. Blockson’s uranium recovery process was a byproduct process 

designed to fit into the existing phosphate process (Stoltz, 1958). The primary 

radionuclides of interest for potential external exposure in a uranium extraction 

process are U-238 and daughter radionuclides Th-234 and Pa-234m. Radiation 

dose rates from uranium and its daughter products are well-documented, and 

bounding estimates for external radiation doses can be reconstructed by 

calculating dose rates to individuals in proximity to the uranium products for a 

bounding amount of time. The dose rates from the extracted uranium would be 

higher than those dose rates encountered by employees who were exposed to 

radioactive materials that were present, but not concentrated, at other locations 

in the process. Therefore, the external doses from the extracted uranium would 

bound doses for all employees.
HHS Special Exposure Cohort Designation: 

Blockson Chemical Company, Joliet, Illinois Page 5

• NIOSH assumes employees received an annual chest X-ray and uses claimantfavorable methods and data to estimate related radiation doses.

• Pursuant to 42 C.F.R. § 83.13(c)(1), the NIOSH Director determined that there is 

insufficient information to either: (1) estimate the maximum radiation dose, for 

every type of cancer for which radiation doses are reconstructed, that could have 

been incurred under plausible circumstances by any member of the class; or (2) 

estimate the radiation doses of members of the class more precisely than a 

maximum dose estimate.

• Although the NIOSH Director found that it is not possible to reconstruct radiation 

doses for the proposed class, NIOSH intends to use any internal and external 

monitoring data that may become available (and that can be interpreted using 

existing NIOSH dose reconstruction processes or procedures) for an individual 

claim. Dose reconstructions for individuals employed at Blockson Chemical, but 

who do not qualify for inclusion in the SEC, may be performed using these data 

as appropriate.

• NIOSH finds that it is feasible to estimate, with sufficient accuracy, occupational 

medical dose for this class of employees using the assumptions and applicable 

protocols in the complex-wide Technical Information Bulletin, Dose 

Reconstruction from Occupationally Related Diagnostic X-Ray Procedures

(ORAUT-OTIB-0006).

• The Board recommended the proposed class for addition to the SEC and the 

NIOSH Director concurred with its recommendation.

 Health Endangerment

The Secretary established the health endangerment determination for the class of 

employees covered by this report based upon the findings summarized below.

(1) Pursuant to 42 C.F.R. § 83.13(c)(3), the NIOSH Director established that there 

is a reasonable likelihood that such radiation doses may have endangered the 

health of members of the class. Pursuant to 42 C.F.R. § 83.13(c)(3)(ii), the 

NIOSH Director specified a minimum duration of employment to satisfy this 

health endangerment criterion as “having been employed for a number of 

work days aggregating at least 250 work days within the parameters 

established for this class or in combination with work days within the 

parameters (excluding aggregate work day requirements) established for one 

or more other classes of employees in the Cohort.”

(2) The Board and the NIOSH Director did not identify any evidence from the 

petitioners or from other resources that would establish that the class was 

exposed to radiation during a discrete incident likely to have involved 

exceptionally high-level exposures, such as a nuclear criticality incident, as 

defined under 42 C.F.R. § 83.13(c)(3)(i). 
HHS Special Exposure Cohort Designation: 

Blockson Chemical Company, Joliet, Illinois Page 6

(3) The NIOSH Director concurred with the Board’s finding that the health of the 

class may have been endangered and defined the class according to the 250-

work day requirement specified under 42 C.F.R. § 83.13(c)(3)(ii). 

IV. Effect and Effective Date of Designation

The Secretary submits this report on the designation of one additional class to the 

SEC for review by Congress, pursuant to 42 U.S.C. §§ 7384l(14)(C)(ii) and 

7384q(c)(2)(A), as amended by the Ronald W. Reagan National Defense 

Authorization Act for Fiscal Year 2005, Pub. L. No. 108-375 (codified as amended in 

scattered sections of 42 U.S.C.). Pursuant to 42 U.S.C. § 7384l(14)(C)(ii), as 

amended by the Ronald W. Reagan National Defense Authorization Act for Fiscal 

Year 2005, Pub. L. No. 108-375 (codified as amended in scattered sections of 42 

U.S.C.), the designation in this report will become effective 30 days after the date of 

this report’s submission to Congress “unless Congress otherwise provides.”

V. Administrative Review of Designation

The health endangerment determination of the designation provided in this report 

may be subject to an administrative review within HHS, pursuant to 42 C.F.R. § 

83.18(a). On the basis of such a review, if the Secretary decides to expand the class 

of employees covered by this designation, the Secretary would transmit a 

supplementary report to Congress providing the expanded employee class definition 

and the criteria and findings on which the decision was based.